Heat exchanger and method of manufacturing same

ABSTRACT

Provided is a heat exchanger having a swirl chamber, an impact chamber and a swirl nozzle connecting the swirl chamber to the impact chamber for directing a swirl spray exiting the swirl nozzle against an impact surface of the impact chamber for outward expansion along the impact surface. The swirl spray impacting the impact surface is a high velocity spray that produces a turbulent flow across the impact surface allowing for increased heat transfer between the impact surface and a heat transfer surface.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 61/425,325 filed Dec. 21, 2010, which is hereby incorporated herein by reference.

FIELD OF INVENTION

The present invention relates generally to heat exchangers, and more particularly to a plate-type heat exchanger having at least one swirl nozzle and at least one impact chamber.

BACKGROUND

Heat exchangers are used for many consumer and commercial products, industrial processes, information systems, and systems for vehicles of all sorts. When designing a heat exchanger, size and/or weight of the heat exchanger are taken into consideration, especially in vehicles such as aircrafts where weight is important for fuel efficiency reasons. For example, for heat exchangers placed in a fan duct area of a turbine engine, the cross-sectional area and length of the heat exchanger are important design considerations because blocking and drag reduce the efficiency of turbine engine, thereby affecting performance and operating costs.

One example of a heat exchanger used in turbine engines is a plate-type heat exchanger. Plate-type heat exchangers use a plurality of plates, such as metal plates, to transfer heat between two fluids. Such a heat exchanger causes the fluids to be exposed to a larger surface area to facilitate the transfer of heat and increase the speed of temperature change.

SUMMARY OF INVENTION

The present invention provides a heat exchanger having a swirl chamber, an impact chamber and a swirl nozzle connecting the swirl chamber to the impact chamber for directing a swirl spray exiting the swirl nozzle against an impact surface of the impact chamber for outward expansion along the impact surface. The swirl spray impacting the impact surface is a high velocity spray that produces a turbulent flow across the impact surface allowing for increased heat transfer between the impact surface and a heat transfer surface.

In particular, the heat exchanger includes as swirl chamber, at least one inlet for tangentially supplying fluid into the swirl chamber, an impact chamber separated from the swirl chamber by a first wall and having a heat exchange wall opposite the first wall forming an impact surface, a swirl nozzle in the first wall connecting the swirl chamber to the impact chamber for directing a swirl spray exiting the swirl nozzle against the impact surface for outward expansion along the impact surface, and at least one outlet for flow of fluid out of the impact chamber.

In one embodiment, the impact chamber includes a radially outer portion in fluidic communication with the at least one outlet.

In another embodiment, the at least one outlet includes a plurality of outlets circumferentially spaced apart and communicating with the radially outer portion of the impact chamber.

In still another embodiment, the swirl chamber is formed in a swirl plate and opens to one side of the swirl plate that is closed by a spacer plate.

In yet another embodiment, the swirl chamber, at least one inlet and the swirl nozzle form a pressure-swirl nozzle, and wherein the swirl plate includes a plurality of pressure-swirl nozzles.

In another embodiment, the impact chamber is formed in an impact plate.

In still another embodiment, the impact plate includes a plurality of impact chambers configured to receive swirl spray from a respective swirl nozzle.

In yet another embodiment, the heat exchanger includes a manifold plate having at least one inlet fluid channel communicating with the at least one outlet and at least one outlet fluid channel communicating with the at least one outlet.

According to another aspect of the invention, a method for heating or cooling a heat transfer surface using a heat exchanger is provided. The heat exchanger includes a swirl chamber, at least one inlet for supplying fluid into the swirl chamber, an impact chamber separated from the swirl chamber by a first wall and having a heat exchange wall opposite the first wall forming an impact surface, and a swirl nozzle in the first wall connecting the swirl chamber to the impact chamber. The method comprises receiving fluid at the at least one inlet, supplying the fluid from the at least one inlet tangentially into the swirl chamber so that a vortex is formed in the swirl chamber, delivering the fluid from the swirl chamber to the swirl nozzle, and directing a swirl spray exiting the swirl nozzle against the impact surface for outward expansion along the impact surface.

The foregoing and other features of the invention are hereinafter described in greater detail with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an exemplary heat exchanger according to the invention;

FIG. 2 is a bottom view of an exemplary manifold plate according to the invention;

FIG. 3 is a top view of an exemplary spacer plate according to the invention;

FIG. 4 is a top view of an exemplary swirl plate according to the invention;

FIG. 5 is a top view of an exemplary impact plate according to the invention;

FIG. 6 is a perspective view of the impact plate according to the invention; and

FIG. 7 is a cross-sectional view of another exemplary heat exchanger according to the invention.

DETAILED DESCRIPTION

The principles of the present invention have particular application to heat exchanges for ground, sea and aerospace vehicles, for example as a heat rejection panel to reject heat in an aircraft to ambient air, and thus will be described below chiefly in this context. It will of course be appreciated, and also understood, that the principles of this invention may be useful in other heat exchangers to exchange heat from a solid, fluid or air to a solid, fluid or air.

Referring now in detail to the drawings and initially to FIG. 1, a heat exchanger 10 is shown having a manifold plate 12, a spacer plate 14, a swirl plate 16 and an impact plate 18, each of which may be formed of one or more layers. The manifold plate, spacer plate, swirl plate and impact plate may be stacked upon one another and coupled in any suitably manner, such as brazing or bonding, for example diffusion bonding, to form a compact high efficiency plate heat exchanger. It will be appreciated, however, that the heat exchanger may be formed as a single plate or by any suitable number of plates having the components described below. It will also be appreciated that a plurality of heat exchangers 10 can be stacked upon one another in any suitable configuration.

The manifold plate, spacer plate, swirl plate and/or impact plate may be made of any suitable material and formed by etching (e.g., chemical etching); conventional machining; electro-chemical machining; micro-machining; forging; casting; molding; punching; forming; positive or negative electro or electro-chemical forming; or rapid prototype and rapid manufacturing, stereolithography techniques such as direct metal laser sintering, selectively laser sintering, selective laser melting, fused deposition, electron beam melting, electron beam freeform fabrication, fused deposition modeling, laminated object manufacturing, laser engineered net shaping, polyjet matrix, selective laser sintering, shape deposition manufacturing, solid ground curing, stereolithography, 3D printing, or robocasting. The plates may, for example be formed as macrolaminate plates formed by etching, where, for example, an etchant may be applied to both sides of the plate(s) and then both sides of the plate(s) may be etched simultaneously.

Turning again to FIG. 1, the heat exchanger 10 includes a swirl chamber 30, at least one inlet 32 for tangentially supplying fluid into the swirl chamber 30, an impact chamber 34, a swirl nozzle 36 connecting the swirl chamber to the impact chamber, and at least one outlet 38 for flow of fluid out of the impact chamber. The impact chamber 34 is separated from the swirl chamber 30 by a first wall 40, which is a bottom wall of the swirl plate 16, and includes a heat exchange wall 42 opposite the first wall 40 forming an impact surface 44. The swirl nozzle 36 is provided in the first wall 40 for directing a turbulent swirl spray, preferably a conical swirl spray and more preferably a hollow cone swirl spray, of fluid exiting the swirl nozzle 36 against the impact surface 44 for outward expansion along the impact surface 44.

The fluid impacting the impact surface 44 is a highly turbulent spray that expands outward in a thin film of active fluid having high velocity and momentum. The spray interacts with and disrupts a boundary layer of fluid on the impact surface 44, which enhances the transfer of heat through the impact plate 18 between a heat transfer surface 46, opposite the impact surface, and the impact surface 44. More particularly, the swirl spray produces a turbulent flow across the impact surface 44 to facilitate transfer of heat to/from the surface from/to the fluid flowing across the surface. The fluid then flows across the surface radially outwardly toward a peripheral region of the impact surface where the outlets 38 are located to drain/remove the fluid. Due to the turbulence of the spray, it will be appreciated that the fluid may be sprayed into air or liquid, for example.

Heat enters the heat exchanger 10 through the heat transfer surface 46 when the heat exchanger is used for cooling and heat exits the heat transfer surface 46 when the heat exchanger is used for heating. In this way, the heat exchanger may transfer heat from a fluid to a solid or from a fluid to another fluid (e.g., by providing two heat exchangers 10 in a stacked arrangement where one mirrors the other).

The fluid is provided to the swirl chamber 30 from the manifold plate 12, which is herein described in detail with reference to FIG. 2. The manifold plate 12 includes at least one inlet 50 coupled to a fluid supply line, at least one outlet 52 coupled to a fluid return line, and a plurality of walls 54 forming a plurality of interdigitated inlet and outlet fluid channels 56 and 58 communicating with the inlet and outlet 50 and 52, respectively. The manifold plate also includes at least one inlet manifold 60 and at least one outlet manifold 62 for delivering fluid from the inlet and outlet to the inlet and outlet channels 56 and 58, respectively. In the illustrated embodiment, the manifold plate 12 includes two inlet manifolds 60 orthogonal to the inlet 50 and two outlet manifolds 62 orthogonal to the outlet 52, although it will be appreciated that any suitable number may be provided.

The plurality of inlet and outlet fluid channels 56 and 58 and the inlet and outlet manifolds 60 and 62 are open to one side of the manifold plate 12 that is closed by the spacer plate 14. It will be appreciated, however, that the manifold plate may be formed having closed channels. Moreover, although shown as being a single layer, it will be appreciated that the manifold plate may be formed as multiple layers, for example as having one layer for the inlet fluid channels 56 and another layer for the outlet fluid channels 58. Additionally, it will be appreciated that the manifold plate may include inlet and outlet fluid channels for two confined fluids, for example when used as a fluid to fluid heat exchanger.

As shown in FIG. 2, the manifold plate includes an inlet fluid channel 56 configured to provide fluid to each of a plurality of swirl chambers 30 formed in the swirl plate 16. Fluid flows into the at least one inlet 50, which may be located near a corner of the manifold plate 12, and into each of the inlet manifolds 60, which are orthogonal to the inlet. The fluid then enters each of the plurality of inlet fluid channels 56 and flows along each channel 56 to the respective inlet(s) 32 for each swirl chamber 30. When fluid exits the plurality of impact chambers 34, the fluid exits via the respective outlet(s) 38 and enters the respective outlet fluid channel 58. The fluid flows along the outlet fluid channels to the outlet manifolds 62, which are orthogonal to the outlet 52. The fluid then flows from the outlet manifolds 62 to the outlet 52, which may be located near a corner of the manifold plate 12, and as shown in an opposite corner to the inlet 50.

Turning now to FIG. 3, the spacer plate 14 includes at least one inlet 70 for delivering fluid to the inlet 32 in the swirl plate 16, and in the illustrated embodiment two inlets 70, each inlet provided to deliver fluid to a respective inlet 32. The spacer plate 14 also includes at least one outlet 72 for receiving fluid from the outlet 38 in the swirl plate 16, and in the illustrated embodiment six outlets 72, each outlet provided to receive fluid from a respective outlet 38. The outlets 72 are circumferentially spaced around the inlets 70. In the illustrated embodiment, at least one of the outlets, shown at reference numeral 76, is spaced around the inlets 70 and the adjacent inlets, shown at reference numeral 78, to receive fluid exiting adjacent impact chambers 34.

The inlets 70 are each in fluidic communication with one of the inlet fluid channels 56 such that fluid flows from the fluid channels 56 to the inlets 70 and then to the inlets 32 in the swirl plate 16. Similarly, the outlets 72 are each in fluidic communication with one of the outlet fluid channels 58 such that fluid flows from the outlets 38 in the swirl plate through the outlets 72 and into the outlet fluid channels 58. It will be appreciated that the inlets and outlets of the spacer plate 14 may be configured in any suitable arrangement.

Turning now to FIG. 4, the swirl plate 16 includes a plurality of pressure-swirl nozzles 80, each pressure-swirl nozzle including a swirl chamber 30, at least one inlet 32, and in the illustrate embodiment two inlets 32, and a swirl nozzle 36. The swirl plate also includes at least one outlet 38, and in the illustrated embodiment, six outlets circumferentially spaced around the inlets 32 in a similar manner as the outlets 74 in the spacer plate 14.

The swirl plate may be a thin plate, such as a suitable macrolaminate plate having a thickness of 0.005 to 0.025 inches, for example. Accordingly, the swirl plate may include a plurality of pressure-swirl nozzles 80 formed as macrolaminated nozzles, for example as described in U.S. Pat. Nos. 5,951,882, 5,740,967 and 5,435,884, which are hereby incorporated herein by reference. Although shown as being one layer, it will be appreciated that the swirl plate 16 may be formed as multiple layers, for example as one layer for each of the inlets 32, the swirl chambers 30 and the swirl nozzle 36. The swirl chambers 30 are open to a first side 82 of the swirl plate 16 and closed by the spacer plate 14, although it will be appreciated that the swirl plate may be formed having closed swirl chambers. The swirl chambers 30 are also coaxial with the respective swirl nozzles 36. The inlets 32 of the swirl plate are circumferentially spaced about an axis of the swirl nozzle 36 to tangentially supply fluid into the swirl chamber 30. If one inlet 32 becomes clogged during operation, fluid may still be supplied to the swirl chamber 30 by the other inlet, allowing operation of the pressure-swirl nozzle to continue. The swirl nozzles 36 may be sized to allow fluid swirling in the swirl chamber to form a vortex and to exit in a shape of a cone, in particular a hollow cone, although it will be appreciated that the swirl nozzles may be configured such that fluid exits in a solid cone.

Turning now to FIGS. 5 and 6, the impact plate includes a plurality of impact chambers 34 separated from respective swirl chambers 30 by the first wall 40. Each impact chamber including a heat exchange wall 42 opposite the first wall 40 forming an impact surface 44. Each impact chamber also includes a radially outer portion 90 in fluidic communication with the at least one outlet 38, and in the illustrated embodiment, in fluidic communication with each of the six outlets 38 surrounding the respective pressure-swirl nozzles 80.

The impact chambers 34 may be formed in any suitable shape, for example a gregorig shaped impact chamber, a circular shaped impact chamber, or other suitable shape having a smooth curve upward which directs the fluid into the outlets 38 in the swirl plate 16 and towards the outlet channels 58. It will be appreciated that although shown as being independent of one another, the impact chambers 34 may be connected to one another, for example, by channels. It will also be appreciated that each impact chamber 34 may include a raised portion (not shown), for example at a center portion of the impact surface.

As noted above, the swirl nozzles 36 direct a swirl cone spray of fluid against the respective impact surfaces 44. The fluid then expands outward along the impact surface 44 to the radially outer portion 90 and then to the outlets 38. The fluid impacting each impact surface disrupts a boundary layer of fluid on the impact surface 44, which enhances the transfer of heat through the impact plate 18 between the heat transfer surface 46 and the impact surface 44. Referring now to FIGS. 1-6, the operation of the heat exchanger 10 is described in detail. Fluid enters the inlet 50 of the manifold plate 12 and flows to each inlet manifold 60. The fluid then flows from the inlet manifolds 60 to each of the plurality of inlet fluid channels 56, and then along each channel 56 to the respective inlets 70 in the spacer plate 14. The fluid then flows through the respective inlets 70 to the respective inlets 32 in the spray plate 16. The fluid is supplied from the inlets 32 tangentially into the respective swirl chambers 30, where the fluid swirls and exits the swirl nozzle 36 in a shape of a cone, in particular a hollow cone. More particularly, the fluid supplied to the swirl chamber swirls creating a thin sheet of fluid with a high tangential velocity. As the sheet hits an exit point of the swirl nozzle 36, the sheet is released from the swirl chamber and expands ballistically. The expansion of the sheet continues rapidly after release from the nozzle, thinning the sheet of fluid until surface tension of the fluid is overcome and the sheet rips into ligaments with the same direction of travel. At the same time, the sheet and ligaments interact with surrounding fluid in the impact chamber creating instabilities that cut the ligaments into smaller drops.

The fluid is directed against the respective impact surfaces 44, for example at a central portion of the impact surfaces, for outward expansion along the impact surfaces 44 toward the radially outer portions 90. The fluid impacting the impact surfaces 44 expands outward in a thin film disrupting the boundary layer of fluid on the impact surfaces 44, which enhances the transfer of heat through the impact plate 18 between the heat transfer surface 46 and the impact surface 44.

The swirl spray produces a turbulent flow across the impact surface 44 radially outward toward the radially outer portions 90 and then exits the impact chambers 34 via the respective outlets 38 in the swirl plate 16. The fluid flows through the outlets 38 and the outlets 72 in the spacer plate 14 to the respective outlet fluid channels 58. The fluid then flows along the channels 58 to the outlet manifolds 62, and then to the outlet 52 in the manifold plate 12 where it exits the heat exchanger. The arrangement of outlets 38 about the periphery of the impact chamber greatly facilitates draining or removing of fluid, such as hot fluid from the impact surface 44.

In this way, a thin, plate-type heat exchanger may be provided that operates in any orientation, for example during rotation of a vehicle, and which provides a highly robust method of cooling the impact surface without requiring precise alignment between swirl nozzles 36 and the impact chambers 34, as would be required by the arrangement disclosed in U.S. Pat. No. 6,519,151. It will be appreciated that the internal configuration of the heat exchanger may be varied throughout the length of the heat exchanger in any suitable manner, for example by varying the size, number, thickness, density, flowrate, and shape of the pressure-swirl nozzles and impact chambers. This will allow the heat exchanger to be designed such that cooling or heating can occur only in desired areas of the heat exchanger to provide a more efficient heat exchanger. Moreover, it will be appreciated that the heat exchanger may be used in a single phase or multi-phase mode.

Turning now to FIG. 7, another exemplary heat exchanger is shown at reference numeral 110. The heat exchanger 110 is substantially the same as the above-referenced heat exchanger 10, and consequently the same reference numerals, but indexed by 100 are used to denote structures corresponding to similar structures in the heat exchanger 110. In addition, the foregoing description of the heat exchanger 10 is equally applicable to the heat exchanger 110 except as noted below. Moreover, it will be appreciated upon reading the present application that aspects of the heat exchangers 10 and 110 may be substituted for one another or used in conjunction with one another where applicable.

The heat exchanger 110 may include a manifold plate 112, a swirl plate 116, a recycle plate 117 and an impact plate 118, each of which may be formed of one or more layers. The manifold plate 112 includes at least one inlet fluid channel 156 for supplying fluid to the inlet slots or fins 132 in the swirl plate, and at least one outlet fluid channel 158 for receiving fluid exiting the swirl chamber 130 as will be described below. The swirl plate 116 includes the swirl chamber 130, at least one inlet slot or fin 132, and in the illustrated embodiment two slots or fins, for tangentially supplying fluid into the swirl chamber 130, a swirl nozzle 136 in a first wall 140 connecting the swirl chamber to an impact chamber 134, and at least one outlet for flow of fluid out of the swirl nozzle 136.

The recycle plate 117 includes an opening 192 for allowing fluid to pass from the swirl nozzle to the impact chamber 134, and a slot 194 having an edge 196 for receiving fluid from the swirl nozzle 136 directing fluid to the outlet 138 to be recycled. The impact plate 118 includes the impact chamber 134, which has a heat exchange wall 142 opposite the first wall 140 forming an impact surface 144 for receiving fluid exiting the swirl nozzle 136. It will be appreciated that the heat exchanger 110 can include a plurality of nozzles 136, impact chambers 134, etc, and such elements may be arranged in any suitable arrangement on the plates.

Fluid enters the heat exchanger 110 via the inlet fluid channel 156 and flows to the inlet slots 132. The fluid is supplied from the inlets 132 tangentially into the respective swirl chambers 130, where the fluid forms a vortex and exits the swirl nozzle 136 in a shape of a cone, in particular a hollow cone. A portion of the conical spray is captured by the slot 194 and a portion of the conical spray passes through the opening 192 and impacts the impact surface 144 at an angle. The captured fluid flows through the outlet 138 and to the outlet channel 158, where it can be recycled. The fluid that impacts the surface 144 enhances the transfer of heat through the impact plate 118 between the heat transfer surface 446 and the impact surface 144, and is driven in one direction across the surface 144 toward a fluid drain.

Although the invention has been shown and described with respect to a certain embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a “means”) used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application. 

1. A heat exchanger comprising: a swirl chamber, at least one inlet for tangentially supplying fluid into the swirl chamber, an impact chamber separated from the swirl chamber by a first wall and having a heat exchange wall opposite the first wall forming an impact surface, a swirl nozzle in the first wall connecting the swirl chamber to the impact chamber for directing a swirl spray exiting the swirl nozzle against the impact surface for outward expansion along the impact surface, and at least one outlet for flow of fluid out of the impact chamber.
 2. A heat exchanger according to claim 1, wherein the swirl chamber is coaxial with the swirl nozzle.
 3. A heat exchanger according to claim 1, wherein the impact chamber includes a radially outer portion in fluidic communication with the at least one outlet.
 4. A heat exchanger according to claim 3, wherein the at least one outlet includes a plurality of outlets circumferentially spaced apart and communicating with the radially outer portion of the impact chamber.
 5. A heat exchanger according to claim 1, wherein the at least one inlet includes a plurality of inlets circumferentially spaced about an axis of the swirl chamber.
 6. A heat exchanger according to claim 1, wherein the swirl chamber is formed in a swirl plate and opens to one side of the swirl plate that is closed by a spacer plate.
 7. A heat exchanger according to claim 6, wherein the swirl chamber, at least one inlet and the swirl nozzle form a pressure-swirl nozzle, and wherein the swirl plate includes a plurality of pressure-swirl nozzles.
 8. A heat exchanger according to claim 7, wherein the swirl plate Includes the at least one outlet.
 9. A heat exchanger according to claim 8, wherein the swirl plate includes at least one outlet adjacent each of the plurality of pressure-swirl nozzles.
 10. A heat exchanger according to claim 6, wherein the spacer plate includes at least one inlet opening for directing fluid to the at least one inlet and at least one outlet opening communicating with the at least one outlet.
 11. A heat exchanger according to claim 1, wherein the impact chamber is formed in an impact plate.
 12. A heat exchanger according to claim 11, wherein the impact plate includes a plurality of impact chambers configured to receive swirl spray from a respective swirl nozzle.
 13. A heat exchanger according to claim 1, further comprising a manifold plate having at least one inlet fluid channel communicating with the at least one inlet and at least one outlet fluid channel communicating with the at least one outlet.
 14. A heat exchanger according to claim 13, wherein the manifold plate includes a plurality of walls forming the inlet and outlet fluid channels, wherein the inlet and outlet are interdigitated.
 15. A heat exchanger according to claim 13, wherein the manifold plate includes an inlet coupled to a fluid supply and communicating with the at least one inlet passage and an outlet coupled to a reservoir and communicating with the at least one outlet passage.
 16. A heat exchanger according to claim 15, wherein the manifold includes at least one inlet manifold for delivering fluid from the inlet to the at least one inlet fluid channel, and at least one outlet manifold for delivering fluid from the at least one outlet fluid channel to the outlet.
 17. A method for heating or cooling a heat transfer surface using a heat exchanger, the heat exchanger including a swirl chamber, at least one inlet for supplying fluid into the swirl chamber, an impact chamber separated from the swirl chamber by a first wall and having a heat exchange wall opposite the first wall forming an impact surface, and a swirl nozzle in the first wall connecting the swirl chamber to the impact chamber, the method comprising: receiving fluid at the at least one inlet; supplying the fluid from the at least one inlet tangentially into the swirl chamber so that a vortex is formed in the swirl chamber; delivering the fluid from the swirl chamber to the swirl nozzle; and directing a swirl spray exiting the swirl nozzle against the impact surface for outward expansion along the impact surface.
 18. A method according to claim 17, wherein the fluid expanding outward along the impact surface flows out of the impact chamber via at least one outlet.
 19. A method according to claim 18, wherein the heat exchanger further comprises at least one inlet fluid channel communicating with the at least one inlet and at least one outlet fluid channel communicating with the at least one outlet.
 20. A method according to claim 17, further comprising: directing a portion of the swirl spray against the impact surface; and capturing a portion of the swirl spray in a slot communicating with at least one outlet. 